A SATELLITE VIEW OF SPATIAL AND TEMPORAL VARIABILITY OF CHLOROPHYLL-a AND SST IN COASTAL PNW WATERS

Kathleen A. Edwards¹ and Barbara M. Hickey²

¹Applied Physics Laboratory, University of Washington, Seattle, WA 98105, USA
²School of Oceanography, University of Washington, Seattle, WA 98105, USA

The razor clam fishery along the coast of the Pacific Northwest has been repeatedly closed by domoic acid poisoning. The production of the toxin by Pseudo-nitzschia species is currently under study by the ECOHAB PNW field program. Results to date suggest that an eddy off the mouth of Juan de Fuca Strait (Fig. 1a) is an initiation site for blooms of toxic Pseudo-nitzschia which are then advected onto the coastal beaches during fall storms. This talk will present results from satellite analysis performed in support of ECOHAB PNW. While the available satellite data (sea surface temperature and chlorophyll-a concentration) do not capture the biological processes behind the toxification of the clams, they provide information about the physical setting in which the toxification has occurred. Statistical analysis is performed on 7 years of SeaWiFS chlorophyll-a data and 18 years of AVHRR SST data in order to characterize the space and time variability of the coastal waters of the Pacific Northwest (Fig. 1a). When a seasonal cycle is fit to the satellite data, the eddy is distinguished from the coastal shelf region by several characteristics. In the eddy, the annual peak in productivity occurs earlier than on the shelves to the north or south (Fig. 1b). The range in SST values over the course of the year is lower in the eddy than on the coastal shelves to the north or south, suggesting that conditions in the eddy are relatively steady; in turn, the annual change in SST for both the eddy and the shelf regions is less than offshore (Fig. 1c). The relationship between variability in the eddy and the coastal shelves and candidate forcing mechanisms, such as wind-driven upwelling or outflow from the Juan de Fuca Strait, will be discussed.